package ljl.codetop300;

/**
 * 这玩意谁会啊
 */
public class _96_num_trees {

  static class dp {
    public int numTrees(int n) {
      int[] dp = new int[n + 1];
      dp[0] = 1;
      dp[1] = 1;

      for (int i = 2; i <= n; ++i) {
        for (int j = 1; j <= i; ++j) {
          dp[i] += dp[j - 1] * dp[i - j];
        }
      }
      return dp[n];
    }
  }

  static class copy_dp {
    public int numTrees(int n) {
      int[] d = new int[n + 1];
      d[0] = d[1] = 1;
      for (int i = 2; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
          d[i] += d[j - 1] * d[i - j];
        }
      }
      return d[n];
    }
  }
}
